A dry developer can be classified into a one component developer using a toner alone, which is formed by dispersing a coloring agent in a binder resin and a two-component developer composed of a mixture of the aforesaid toner and a carrier. An electrostatic latent image formed on a photoreceptor, etc., is developed by the aforesaid developer and after transferring the toner image formed to a transfer sheet or paper, toners remaining on the photoreceptors are cleaned. Accordingly, the dry developer is required to meet various conditions in the photocopying step, in particular, the development step or the cleaning step. In particular, a toner is used for the development as each particle without the aggregate thereof at development, and for the purpose, it is necessary that the toner has a sufficient fluidity and also the fluidity or the electric property thereof does not change with the passage of time or by the change of environmental conditions (e.g., temperature and humidity). Also, in the two-component developer, it is required that the developer does not cause so-called toner filming, i.e., a phenomenon of sticking the toner onto the carrier surface.
Furthermore, the toner is required to have such cleaning properties that the remaining toners can be easily removed from the surface of the photoreceptor at cleaning and that when a cleaning member such as a blade, web, etc., is used for cleaning the remaining toners, they do not injure the surface of the photoreceptor.
For meeting these requirement, as a dry developer, various one-component developers or two-component developers prepared by adding an inorganic fine powder such as silica, etc., an organic fine powder such as a fatty acid or a derivative or metal salt thereof, etc., a fine powder of a fluorine series resin, etc., to a toner have been proposed to improve, thereby, the fluidity, the durability, or the cleaning property thereof.
However, in the conventionally proposed additives for toners, an inorganic oxide such as silica, titania, alumina, etc., greatly improves the fluidity of the developer but since the inorganic oxide itself is considerably hard, there are problems that they dent and injure the surface of the photoreceptor and as a result, the toners stick to these portions.
Also, for an organic belt photoreceptor for a high-speed copying machine, a cleaning system using a rubber blade or a brush is employed but as compared to the cleaning system for a conventional drum photoreceptor, the cleaning performance is greatly reduced by the distortion, bending, etc., of the organic belt photoreceptor, and in particular, there sometimes occurs that a paper dust, etc., enters between the photoreceptor and the blade to cause poor cleaning.
Furthermore, recently, a requirement for a low-potential high-developing property has been increased, and thus, low-specific gravity low-magnetic force dispersion type carriers composed of a resin and a magnetic powder as essential components have been used. However, such a carrier has a problem that the carrier is liable to attach to the surface of the photoreceptor and injures the surface of the photoreceptor at cleaning.